The current state of the corruption tileset is mostly due to painting myself into a corner within the limited timeframe. At first I wanted it to be mostly dark grey, but then when I started drawing enemies their black ended up being too hard to see. I tried adding outlines to the enemies but it didn't look great, so I brightened the corruption instead, and it ended up being green to help the purple bullets stand out more. I did lower the contrast and brightness a couple times, but I guess it only helped a little.
If I were to expand this project I'd get an actual artist to draw some enemies that aren't featureless black shapes so I could make the corruption mostly dark again, which would probably be much easier to look at.